Linear Acoustic Modelling using 1-D Flow Systems which represent Complex 3-D Components 2011-01-1524

Acoustics of automotive intake and exhaust systems have been modelled very successfully for many years using 1D gas dynamic simulations. These use pseudo 3D models to allow complex components to be constructed from simple building blocks. In recent years, tools have appeared that automate the construction of network models from 3D geometries of intake and exhaust components. Using these tools, concurrent noise and performance predictions are a core part of most engine development programmes. However, there is still much interest in the more traditional field of linear acoustics: analysing the acoustic behaviour of isolated components or predicting radiated noise using a linear source. Existing approaches break the intake and exhaust system down into a set of components, each with known acoustic properties. They are then connected together to create a network that replicates the donor non-linear model. A new approach is used whereby the exact same network representation is used for both linear and non-linear analysis of the model. Each modelling element in the non-linear model directly corresponds to an element in the linear model. There is no prior knowledge of the intention of the geometry (resonator, etc). The acoustic behaviour is an output (measured) rather than an input (assumed). The core of this new approach is the conversion of complex 1-D flow networks to their acoustic equivalents. Comparisons of predicted transmission loss between full non-linear simulations and the new linear model show close agreement for a large range of auto-meshed 3D components.